Nonblocking nonwoven scrim materials

ABSTRACT

A nonwoven scrim material that may be wound up on a roll without the development of any significant degree of blocking by employing a polyvinyl chloride plastisol adhesive fused beyond its point of residual tack and having a surface level of plasticizer within certain critical limits, and methods for forming such materials.

United States Patent Condon 1 Mar. 28, 1972 NONBLOCKING NONWOVEN SCRIM MATERIALS Inventor: Eugene H. Condon, Neenah, Wis.

Kimberly- Clark Corporation, Neenah, Wis.

Filed: Mar. 7, 1969 Appl.No.: 805,243

Assignee:

US. Cl ..161/57, 117/76 T, 156/174, 156/175, 161/143, 206/59 A Int. Cl ..D04h 3/02, D04h 3/12 Field of Search ..206/59 A; 117/76 T; 161/57, 161/58, 92,143, 144, l75;156/173,174, 125

References Cited UNITED STATES PATENTS 9/1959 Hirschy et a1 ..161/57 2,939,200 6/1960 Ewing et a1. ..161/143 X 3,067,059 12/1962 Jannarelli et a1 ..117/76 T 3,072,511 1/1963 Harwood. ..161/57 X 3,072,512 1/1963 Dalle ..161/89 3,285,798 11/1966 Tesoro ..161/92 3,307,992 3/1967 Condon 61:111.... 161/143 X Primary Examiner-Robert F. Burnett Assistant Examiner-Raymond O. Linker, Jr. AttorneyWolfe, Hubbard, Leydig, Voit & Osann [5 7] ABSTRACT A nonwoven scrim material that may be wound up on a roll without the development of any significant degree of blocking by employing a polyvinyl chloride plastisol adhesive fused beyond its point of residual tack and having a surface level of plasticizer within certain critical limits, and methods for forming such materials.

2 Claims, 7 Drawing Figures P'A'TENTEllmR'aa 1972 sum 1 [IF 2 NONBLOCKIING NONWOVEN SCRIM MATERIALS This invention relates to nonwoven materials and, more particularly to nonwoven scrim materials characterized by their ability to be wound up and stored for considerable periods of time without any significant blocking.

In recent years, nonwoven materials have come into widespread use, particularly where a product is designed to be used only once or for a relatively few number of times. Surgical gowns, laboratory coats, disposable sheets, towelling, and wipes are typical examples.

One material that may be advantageously employed in such uses is a scrim comprised of one set of warp threads running in the machine direction and a set of transverse or fill threads in face-to-face contact with the warp threads. The two sets of threads are adhesively bonded to each other at the thread crossings. The scrim is typically employed as an economical reinforcing layer for one or more plies of a weaker material such as cellulosic wadding that can be bonded to one or both surfaces of the scrim. This provides an economical laminate of adequate strength characteristics for a wide variety of uses. The scrim may also be combined with a fiber applique to provide a strong material with superior softness and aesthetic characteristics.

Heretofore, the formation of the scrim and the combination with another material to form a laminate has been carried out together due to the difficulties in winding up a scrim material. More specifically, in the past when it was desired to wind up a scrim for either transportation or storage, it was found necessary to either sprinkle a material such as talc between adjacent windings or to place a release liner or the like between adjacent layers. If these or similar steps were not taken, adjacent layers would at least partially fuse together and unwinding the roll would result in significant degradation and destruction of the scrim. More specifically, at least some of the scrim layers would be partially fused together by the adhesive used to bond the scrim threads together and unwinding would literally rip apart some of the previously bonded crossed threads.

It is an object of the present invention to provide nonwoven scrim materials which may be easily wound up on rolls and stored for a considerable period of time without the development of any significant blocking.

It is another object of the present invention to provide an economical method for forming nonwoven scrim materials of the hereinbefore described type.

Other objects and advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. l is a schematic view of apparatus that may be employed for forming the nonblocking scrim of the present invention;

FIG. 2 is a schematic view illustrating slightly modified apparatus that may be employed for forming nonblocking scrim;

FIG. 3 is a schematic view illustrating a still further type scrim apparatus that may be advantageously employed;

FIG. 4 is a photomicrograph of a portion of a nonblocking scrim and illustrating the distribution of adhesive;

FIG. 5 is a photomicrograph of a cross section of warp threads and further illustrating the distribution of adhesive relating to the scrim threads;

FIG. 6 is a photomicrograph of a portion of a nonblocking scrim in which a first adhesive is coated with an external coating of a plastisol adhesive; and

FIG. 7 is a photomicrograph of a warp thread printed with the two adhesives as described in connection with FIG. 6 and further illustrating the distribution of the adhesive with respect to the thread.

While the invention is susceptible of various modifications and alternative forms, certain specific embodiments thereof have been shown by way of example in the drawings which will be described in detail herein. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but, on the contrary, the intention is to cover all modifications, equivalents and alternative forms falling within the spirit and scope of the invention.

Turning to the drawings, FIG. it illustrates one embodiment for forming a nonwoven nonblocking scrim. Thus, a plurality of machine direction or warp threads 10 are constantly being supplied from a creel (not shown) and are guided through an adhesive applicator roll 12 having rounded bottom V-grooves which receive and guide the threads. The roll 12 rotates in a pond of adhesive coating composition 141. The grooves are flooded with adhesive and the threads are submerged so that the adhesive can coat the entire periphery of the threads.

In accordance with the present invention, scrim that may be wound up on rolls without development of blocking is achieved by insuring that the scrim threads have an exterior coating of a polyvinyl chloride adhesive with a plasticizer level at the outer surface prior to wind up which is controlled within narrow critical limits.

To this end, the present invention achieves nonblocking scrim by employing a plastisol adhesive in which the resin may be either a polyvinyl chloride homopolymer or a copolymer of polyvinyl chloride with other materials such as polyvinyl acetate or acrylics in which the content of the polyvinyl chloride is above about percent by weight. The plasticizer may be any of the conventionally used ones. Organic phthalates such as butyl benzyl phthalate, sebacates such as dioctyl sebacate and adipates are representative examples. A minor amount of a tackifying agent (i.e., generally between 3 and 7 parts per parts resin) may also be included. Materials which may be employed as tacltifying agents include carboxylated polyvinyl chloride-polyvinyl acetate copolymers, rosin esters such as hydrogenated esters of rosin and pentaerythritol esters of rosin.

It is critical that the plasticizer level at the coating surface of the formed scrim be maintained within the range of from about 50 to 70 parts per 100 parts of the plastisol resin. This critical level may be obtained by formulating the adhesive composition supplied to the applicator roll 12 with a plasticizer level as hereinbefore set forth. The resulting scrim will have a distribution of adhesive relative to the threads as shown in the photomicrographs of FIGS. 4 and 5. The threads are completely coated about their periphery with a substantially uniform coating.

Alternatively, the adhesive applicator could coat a latex or solvent-based adhesive onto the warp threads and the warp threads could then subsequently be coated with a polyvinyl chloride plastisol. In this instance, the plasticizer level should be maintained in the range of from about 35 to about 70 parts per 100 parts resin. This results in a scrim as shown in the photomicrographs of FIGS. 6 and 7. The warp threads have an inner coating of polyvinyl acetate and a polyvinyl chloride adhesive layer (formulated in accordance with the present invention) encapsulates the inner coating of the polyvinyl acetate. It can readily be seen that the introduction of the polyvinyl acetate provides more irregularities in the coating than does the plastisol.

It should also be appreciated that it is the level of plasticizer at the exterior surface of the adhesive coating which must be maintained within the critical limits. Accordingly, nonblocking scrim, i.e., scrim which can be wound up on a roll without introducing any foreign materials between adjacent layers and subsequently unwound without significant disruption or tearing apart, may be obtained by employing techniques which create different zones or gradients of plasticizer level. For example, the plastisol formulation may incorporate a material that modifies the surface plasticizer level only, by absorption or by employing a plasticizer that has a tendency to migrate from the surface.

The thus-coated threads are then forwarded onto the surface of a moving belt such as a silicone rubber endless belt 16 and are guided about a stationary cylindrical mandrel 18 so as to form a series of helices. The belt 16 is continuously pulled about the stationary mandrel 18 by means not shown. A rotating carrier or disc 20 applies cross direction or fill threads 22 to the moving web of threads in a direction normal to the direction of the previously applied threads. The carrier 20 is accordingly arranged to wrap additional threads in the form of helices at right angles to the helices formed by the previously deposited machine direction or warp threads as those threads pass about the mandrel 18. The belt 16 is heated so that the tack of the adhesive on the warp threads will be increased sufficiently so that the till threads will readily adhere thereto.

To form the scrim, the threads are slit as they exit from the mandrel. A slitter 14 thus engages the crossed threads to sever the cross strands parallel to the marginal edge of the moving sheet of threads as the belt 16 is removed from the mandrel to form a scrim 26.

The scrim may then be separated from the crosslayer belt 16 by heating to a sufficient temperature that the adhesive will release from the silicone rubber belt. The scrim 26 is accordingly passed through a hot box or oven 28 maintained at a temperature in the range of from about 300 F. to 350 F. In addition to providing for separation of the scrim from the crosslayer belt, the belt will generally be heated sufficiently so that the desired tack of the adhesive, as hereinbefore described, will be developed.

In some situations, it may be desirable to add additional adhesive to fill and/or warp threads. As shown, the scrim passes under a turn roll 30 and adhesive is first applied to the warp side by rolls 32 and then to the fill side by rolls 34. Referring again to FIGS. 4 and 6, the difference in thickness of the adhesive coating resulting from the two applications of adhesive to the warp threads as contrasted with the single application to the till threads is apparent.

To bring the adhesive past its point of residual tack, the scrim is passed around one or more hot rolls. As shown, the scrim 26 is passed around heated rolls 36 which are maintained at temperatures in the range of 300 to 350 F. for a period of time sufficient to heat the plastisol adhesive to within 20 of its fusion point (i.e., beyond the state of residual tack) and wound up on roll 38.

In accordance with one feature of the present invention, the scrim that is wound up on the roll may be stored for a considerable period of time without the development of any significant amount of blocking. To insure that blocking will not result, the scrim should be allowed to cool below about 90 F. and preferably close to ambient conditions, and then wound up with a minimum amount of tension. Desirably, the tension is such that there is a slight slack in the scrim as is being wound.

FIG. 2 illustrates another type of apparatus that may be used for forming the nonblocking scrim of the present invention. In this and in FIG. 3, the same elements will be given the same numbers with primes being added for distinction. The scrim 26' coming from the crosslayer is passed through a hot box 28' to allow the scrim to be separated from the crosslayer belt 16. The scrim 26 is then partially wrapped about an internally heated roll 40 maintained at a temperature in the range of from about 300 to 350 F. and provided with a release surface such as chrome. The degree of wrap should be sufficient to allow the plastisol adhesive to flow to increase the thread-to-t.hread bond strength. As in the previous embodiment, if desired, additional adhesive may be applied to the warp and fill threads, respectively, by rollers 32' and 34'. Similarly, the scrim may then be passed around hot rolls 36 and wound up on roll 38 with the temperature and tension being maintained as hereinbefore described. The contact of the scrim with the hot roll 40 provides increases in the bond strength between the warp and fill threads of 10 or 15-fold.

FIG. 3 illustrates an additional modification. In this embodiment, the scrim is separated from the crosslayer belt after the adhesive has been brought to its elastomeric point, i.e., the point at which the adhesive begins to act as a film and has a little elastic strength. As shown, the scrim 26 and the crosslayer belt 16 are partially wrapped about a hot roll 41 to provide sufiicient residence time for the adhesive to allow release from the surface of the hot roll. As in the previous figures, the warp and fill threads may then be provided with additional adhesive by rollers 32" and 34" and passed around hot rolls 36". The scrim may then be wound up on roll 38" as hereinbefore described.

Thus, as has been seen, the present invention provides a scrim that may be wound up without the use of any liner or other means of separation between adjacent layers without the development of blocking. This allows the scrim to be manufactured in one location, wound up and then shipped to another location, if desired, for combination with other materials to form a variety of laminates.

I claim as my invention:

1. A nonwoven scrim comprising two sets of spaced threads disposed in face-to-face relation to each other with the threads of one set extending transversely of those of the other set and wholly on one side thereof, at least one set of threads having a substantially continuous surface coating around the thread periphery of an adhesive selected from the group consisting of solvent-based and latex, the sets of threads being bonded to each other at their crossover points and a plastisol adhesive forming a continuous coating around the other adhesive, the plastisol adhesive including a resin selected from the group consisting of polyvinyl chloride homopolymers and the polyvinyl chloride copolymers containing at least about percent by weight polyvinyl chloride, a plasticizer and a tackifying agent, the plasticizer content at the surface of the coating being between about 35 to about 70 parts per parts resin, the plastisol being fused beyond its point of residual tack, said scrim being capable of being wound upon itself in roll form and subsequently unwound without significant disruption.

2. The nonwoven scrim of claim 1 wherein the adhesive is polyvinyl acetate. 

2. The nonwoven scrim of claim 1 wherein the adhesive is polyvinyl acetate. 